1. Field of the Invention
The present invention relates to technology for analyzing noise of an integrated circuit by use of a computer, and specifically relates to a noise analysis system and a noise analysis method to analyze crosstalk noise generated in wires of the integrated circuit.
2. Description of the Related Art
In an integrated circuit, since a transistor with low output impedance has a large driving capability, the waveform of a signal transmitted from such a transistor tends to generate significant crosstalk noise in a signal propagated through an adjacent wire. On the contrary, since a transistor with high output impedance has a low driving capability, the waveform of a signal transmitted from such a transistor is subject to the influence of crosstalk noise. With increased integrated circuit density, the crosstalk noise, which causes a malfunction of a logic circuit, has been a significant problem.
In a conventional crosstalk noise analysis method, a criterion for judging or determining generation of crosstalk noise is whether the crosstalk noise inverts the logic of a receiver cell in a state where a constant signal (high or low signal) is being propagated (hereinafter, referred to as “a static state”) through a wire.
However, the conventional crosstalk noise analysis method does not take into consideration the influence of crosstalk noise in a state where a rising or falling signal is being propagated (hereinafter, referred to as “a transition state”). In some cases, crosstalk noise does not cause a malfunction of the receiver cell in the static state while crosstalk noise is generated in a rising or falling signal propagated through the wire and causes a malfunction of the receiver cell in the transition state. Therefore, the conventional crosstalk noise analysis method cannot completely prevent a malfunction of the receiver cell. In this specification, the “rising signal” and “falling signal” is not limited to rising and falling sections of a rectangular wave signal such as the leading and trailing edges of a clock pulse, but also represent the rising and falling signals propagating in wires, respectively.
It is also possible to equally estimate the influence of crosstalk noise in the transition state using the crosstalk noise in the static state as the criterion to change the design. However, such design change leads to a large circuit design, thus increasing the circuit area and power dissipation and reducing speed of the circuit.